Effect of martensite on cold cracking in 600-MPa grade flux-cored arc weld metals using the Y-groove test

Abstract

This study observed the cold crack susceptibility of three types of low-hydrogen flux-cored arc (FCA)-weld metals developed for a yield strength of 600 MPa. Cold cracks in the weld metal were measured using the Y-groove test, and four different preheating temperatures were employed from room temperature to 150 °C. The microstructure of the Y-groove weldment consisted of acicular ferrite, bainite, and martensite. All weld metals showed cold cracking at room temperature, and a preheating temperature of 50 °C produced cold cracking only for weld metal C, having the largest carbon equivalent and the largest volume fraction of bainite and martensite. The volume expansion ratio of the weld metals was measured when the austenite was transformed to martensite during simulated weld cooling. Weld metal C showed the largest volume expansion ratio (2.6 %), resulting in the largest probability of cold crack production. Moreover, the martensite affected the cold crack fractography in the weld metal. Intergranular fracture occurred in the region occupied by large volume fractions of martensite, and quasi-cleavage fracture was observed in regions of small-volume fractions of martensite. Large amounts of martensite were related to the regions of high Mn content and corresponding to intergranular fracture.